Such an emulsifier and coffee-making apparatus are known from European patent application 0,243,326.
This known emulsifier is often used in coffee-making apparatuses for professional use, that is, in the catering industry. In this apparatus, for the purpose of preparing cappuccino, first an amount of coffee extract, that is, black coffee, is introduced into, for instance, a cup. Then, using the emulsifier, an amount of frothed milk is supplied to the cup.
For preparing the frothed milk, an amount of steam is supplied under pressure to the first steam inlet. This steam will move to the first suction chamber. As a result of the venturi effect, a reduced pressure will be created in the first suction chamber, as a result of which air is sucked to the first suction chamber via the air inlet and milk is sucked to the first suction chamber via the first milk inlet. The united air, milk and steam then move from the first suction chamber to the mixing chamber to be properly mixed there, so that frothed milk of a good quality is obtained. Via an outlet of the mixing chamber, frothed milk can thereupon leave the emulsifier to be supplied, for instance, to the cup.
It is desired to be able to prepare not only frothed milk, but also hot, non-frothed milk, for instance for the purpose of obtaining `cafe au lait`. To that end, the emulsifier according to European patent application 0,243,326 comprises a controllable valve with which the air inlet can be shut off, the idea being that when no air is supplied to the suction chamber and so only milk and steam are supplied to the suction chamber, the emulsifier will not dispense hot milk that frothes. A problem presents itself, however, in that such an apparatus is rather costly. Moreover, it appears that directly after the air inlet is shut off, yet milk that frothes slightly is dispensed. Also, a temperature problem arises in that the tube passage is unchanged. A further disadvantage is that the emulsifier must be operated by hand and is not adapted for automatic, remote operation for the selection between hot milk or hot frothed milk.